Abstract: To drive a liquid crystal panel without producing flickering or noise on a screen, an adder circuit 26 adds the noise component of the analog signal detected in a filter 24 to a reference voltage from a power supply 16, and a phase adjustment circuit 28 adjusts the phase of the reference voltage to which the noise component was added. A circuit 12 holds the analog signal and outputs it to comparators 14.sub.1 to 14.sub.n. The reference voltage from the circuit 28 is divided in resistors 18.sub.1 to 18.sub.n+1 and output to comparators 14.sub.1 to 14.sub.n as threshold voltages TV.sub.1 to TV.sub.n. The comparator 14 compares the input analog signal to the voltage TV, and outputs a predetermined signal to an encoder 20 if the analog signal is greater than the voltage TV. The encoder 20 converts the signal from the comparator 14 to a digital signal and applies it to the electrode of a liquid crystal panel.

Abstract: In order to drive a liquid crystal panel without causing flickering or noise on a screen, an analog signal (R) is input to sample and hold circuits SH through an amplifier 14. When the first half of the clock signals is input, the voltage values of the analog signal which are held in the corresponding circuits SH1 . . . SH(n/2) are added up in an adder 16, divided by n/2 in a divider 18, and output to a circuit SH(n/2+1). When the second half of the clock signals is input, the voltage values which are held in the corresponding circuits SH(n/2+2) . . . SH(n+1) are added up in an adder 16', divided (by n/2) in a divider 18', and output to a circuit SH(n+2). The outputs from the circuits SH(n/2+1) and SH(n+2) are summed in an adder 24 and divided by 2 in a divider 26. A driver circuit applies a voltage to the corresponding electrode of a liquid crystal panel according to the output from the divider 26.

Abstract: A key actuated secure docking apparatus for a portable computer locks the apparatus so that internal electronic devices are prevented from being detached from a base body of a docking apparatus, even if the desktop base is left without a docked portable computer. Further, the key mechanism allows the docking apparatus to be placed in a condition in which power supply for the docking apparatus cannot be turned on even if the power switch for the power supply is turned on. Data in a storage device internal to the docking apparatus cannot be stolen or destroyed by attempting docking with a portable computer since power is not supplied to the storage device.

Abstract: A filter has a plurality of series circuits each including a reactance element and a switching element and the series circuits are connected in parallel. The switching elements are driven by clock pulses of the same period. When the switching elements are driven simultaneously, information stored in the reactance elements is cleared, whereby the filtering band can be switched over at high speed.